Cellulose fiber materials tend to deteriorate when subjected to elevated temperatures for extended periods of time, resulting in a progressive reduction in their strength until eventual fracture occurs. Cellulose insulation materials are used extensively in electrical apparatus and during use are subjected to elevated temperatures. In electrical apparatus, such as transformers for example, the rate of deterioration is further increased because the cellulose insulation is in contact with, or immersed, in a liquid dielectric, such as transformer oils. Elevated temperatures cause the liquid dielectrics to decompose and the resultant products of decomposition, in turn, attack the cellulose insulation. For this reason cellulose insulation materials in contact with liquid dielectrics generally deteriorate at a far greater rate than cellulosic material not in contact with such liquids.
The problem of deterioration of cellulose fiber material at elevated temperatures is also encountered when using cellulose fiber cord reinforcing in rubber articles, such as pneumatic tires, steam hoses, conveyor belts, and the like. In this situation, the cellulose fiber reinforcement which is subjected to elevated temperatures either from external heat or from heat generated internally by reason of repeated flexing, as in the case of pneumatic tires, tends to deteriorate, resulting in a progressive reduction in the strength of the cellulose fiber reinforcement.
Deterioration of cellulose fiber material at elevated temperatures is also encountered in calendar rolls used in the papermaking industry. Calendar rolls are usually formed of a series of laminated, annular, or layers of paper and during use, the calendar roll is subjected to a hot air environment along with mechanical stressing which can cause rapid deterioration of the cellulosic material.